We have been investigating autonomous and non-autonomous pathways that specify embryonic cell fate and pattern formation using Dictyostelium discoideum as an experimental system. In Dictyostelium, stimulation of a family of 7-span receptors by the secreted morphogen cAMP establishes the fundamental anterior (prestalk) / posterior (prespore) developmental axis. cAMP receptor (CAR) subtypes 3 and 4 have antagonistic affects on the enzymatic activity of the cytoplasmic protein kinase GSK3. CAR3 is coupled to an activation pathway for GSK3 regulation and prespore differentiation, whereas CAR4 inhibits GSK3 and, thus, promotes prestalk differentiation. Consistent with these biochemical data, car4-null cells and gsk3-null cells have substantially opposite developmental phenotypes. car4 nulls are inhibited in prestalk differentiation, while gsk3-nulls have prespore defects. The car4-null phenotype can be rescued by co-expression of a dominant-negative GSK3, supporting the upstream, inhibitory function for CAR4 in control of GSK3 and subsequent prestalk/prespore fate decisions. This pathway parallels that of the 7-span Frizzled (Wnt/Wg) receptors in control of GSK3 activity and dorsoventral axis formation in Xenopus. We have established both G protein dependent and G protein independent pathways for cAMP signalling via the 7-span CARs, and are now attempting to determine if CAR regulation of GSK3 requires a productive G protein interaction. Like CAR4, the RING/zipper protein rZIP inhibits prespore, but promotes prestalk differentiation. Using cell-specific markers and developmental chimaeras of wild-type and rZIP-nulls, we show that rZIP functions non-autonomously to inhibit a prespore activation gradient, but autonomously via the gradient to localize prespore expression. Studies of cells that hyperexpress the catalytic subunit or a dominant-negative regulatory subunit of the cAMP-dependent protein kinase (PKA), suggest a genetic interaction of rZIP with PKA to mediate the prespore morphogen gradient. Similar to the metazoan JAKs, the ZAK1 tyrosine kinase of Dictyostelium has two kinase homology domains, but may be sufficiently diverged to suggest that it is functionally distinct. Cells that lack ZAK1 are competent to induce prestalk/prespore pathways, but are morphologically deranged and unable to complete terminal differentiation. The zak1-nulls also lack a major, developmentally regulated phosphotyrosyl-containing protein of approximately 100kDa. Experiments are in progress to define this presumptive substrate of ZAK1 and to ascertain its role in the developmental program. At the nuclear level, the chromatin remodeling protein CHD is required autonomously for the differentiation of a population prestalk cells, which, in turn, produce a signal required non-autonomously for induced prespore gene expression.